Re: [PATCH Part2 RFC v4 27/40] KVM: X86: Add kvm_x86_ops to get the max page level for the TDP

[Brijesh Singh]

On 7/20/21 2:38 PM, Sean Christopherson wrote:
...

> The other option is to use vm_type, which TDX is already planning on leveraging.
> Paolo raised the question of whether or not the TDX type could be reused for SNP.
> We should definitely sort that out before merging either series.  I'm personally
> in favor of separating TDX and SNP, it seems inevitable that common code will
> want to differentiate between the two.

Yes, I did saw that and it seems much better.

> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flkml.kernel.org%2Fr%2F8eb87cd52a89d957af03f93a9ece5634426a7757.1625186503.git.isaku.yamahata%40intel.com&data=04%7C01%7Cbrijesh.singh%40amd.com%7Cb658fcf339234fd9030d08d94bb5edf1%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637624067039647374%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=tdVALNsQGer0Z69%2FyYaRqWYZvH27k%2BmgHdslQlJ7qlU%3D&reserved=0

...

> > There is yet another reason why we can't avoid the PSMASH after doing
> > everything to ensure that NPT and RMP are in sync. e.g if NPT and RMP
> > are programmed with 2mb size but the guest tries to PVALIDATE the page
> > as a 4k. In that case, we will see #NPF with page size mismatch and have
> > to perform psmash.
>
> Boo, there's no way to communicate to the guest that it's doing PVALIDATE wrong
> is there?

if the guest chooses smaller page-size then we don't have any means to 
notify the guest; the hardware will cause an #NPF and its up to the 
hypervisor to resolve the fault.

However, if the guest attempts to validate with the larger page-level 
(e.g guest using 2mb and RMP entry was 4k) then PVALIDATE will return 
SIZEMISMATCH error to the guest.

thanks